The present invention relates to the field of non-invasive blood pressure measurement, and more particularly to a method and apparatus for automatically identifying a given one of a predetermined plurality of non-invasive blood pressure cuffs employable in a sphygmomanometric system.
The use of automated sphygmomanometers for the measurement of blood pressure typically entails the placement of an inflatable cuff about an arterial vessel of a body appendage, e.g. the upper arm of a patient. The cuff contains an inflatable bladder which is positioned around the appendage and inflated via an air pump. The inflated bladder provides a constricting pressure against the blood inside the artery. The inflation pressure is generally established to be above a patient""s systolic pressure and should serve to partially occlude the artery. After inflation, gas may be slowly bled from the inflated cuff to gradually reduce the pressure acting upon the artery. During deflation, pressure perturbations, or oscillometric pulses, generated by the partially-occluded artery may be transmitted through the cuff gas supply line for sensing. The sensed pulses may then be analyzed to allow for calculation of the systolic, diastolic and/or mean arterial pressure(s) of a patient, as well as the heart rate of a patient.
It should be noted that, if the pressure of the inflated cuff significantly exceeds a patient""s systolic pressure, blood flow may be unacceptably impeded for purposes of obtaining meaningful measurements. Additionally, high inflation pressures may cause patient discomfort. On the other hand, if the cuff pressure is insufficient, arterial occlusion may be insufficient to yield oscillometric pulses in a pressure range that allows accurate measurements to be taken.
As will be appreciated, the initial inflation pressure desirable for a given patient (e.g. to achieve the desired arterial occlusion) will depend upon the physical attributes of the patient. Specifically, the desired inflation pressure will normally increase with the size of the patient.
The establishment of the desired cuff pressure is closely correlated to the size of a given cuff (e.g. the circumference thereof). It is important to use a cuff which is large enough to distribute the bladder over a relatively large surface area so that the resulting inflation pressure will be largely uniform. Thus, a properly fitted cuff on an adult will be larger than a properly fitted cuff on a child, and a properly fitted cuff on a child will be larger than a properly fitted cuff on a neonate.
In this regard, it is recognized that medical personnel will generally select the cuff size deemed most appropriate for a given patient. It is also recognized that for the given cuff size selected by medical personnel there will be a corresponding inflation pressure, or range of pressures, desirable for achieving the above-noted partial arterial occlusion appropriate for blood pressure measurement.
In view of the foregoing, a primary objective of the present invention is to provide a method and apparatus that provides for the automatic identification of a given one of a predetermined plurality of non-invasive blood pressure cuffs employed in a given blood pressure measurement procedure. Such identification facilitates selection of a desirable initial inflation pressure to be utilized in the blood pressure measurement procedure.
An additional objective of the present invention is to provide for automatic cuff identification in a manner that does not compromise the flexibility or application of the blood pressure measurement system.
Yet a further objective of the present invention is to provide for automated cuff identification in a manner that is both convenient and reliable.
One or more of the above objectives and additional advantages are realized in the inventive method and apparatus of the present invention that provide for a cuff identification operation prior to a blood pressure measurement procedure. The inventive method includes the steps of inflating, at least partially, an inflatable cuff in a pneumatic circuit by flowing gas thereinto; and deflating, at least partially, the inflatable cuff by passing at least a portion of the gas out of the inflatable cuff. The method further provides for the obtainment, during the deflating step, of at least one gas pressure measurement in the pneumatic circuit. Such gas pressure measurement may then be utilized to identify the inflatable cuff being utilized. Preferably, the gas pressure measurement is obtained downstream of the inflatable cuff.
In conjunction with the inventive method, a first pressure measurement means may be employed in the pneumatic circuit to obtain the downstream pressure measurement(s), and the deflation step may further provide for the passage of the gas through a gas-flow restriction means (e.g. a member having a shaped orifice therethrough) interconnected with the pneumatic circuit upstream from the first pressure measurement means. More particularly, the gas-flow restricting means may be located downstream from the inflatable cuff, and fixedly interconnected therewith. In the later regard, it should be noted that each of a predetermined plurality of inflatable cuffs employable with the present invention may be provided with a corresponding different one of a predetermined plurality of corresponding gas-flow restrictors, wherein each of the restrictors serves to restrict, or resist, gas flow therethrough to a differing, discernable degree, thereby facilitating automatic cuff identification.
In a related aspect of the inventive method, the deflation step may provide for both the passage of the gas through a first gas-flow restriction means that is located in the pneumatic circuit upstream from the first pressure measurement means and downstream from the inflatable cuff (e.g. fixedly interconnected therewith), and the passage of the gas through a second gas-flow restriction means interconnected with the pneumatic circuit downstream of the first pressure measurement means. The deflation step may also provide for the selective opening of a bleed valve located in the pneumatic circuit downstream of the second gas-flow restricting means, e.g., wherein the bleed valve may be controlled to provide for a gradual, linear release of gas from the pneumatic circuit. In the later regard, it should be noted that second gas-flow restricting means may actually comprise a bleed valve that is operable to provide a desired degree of gas-flow resistance when opened, thereby obviating the need for a separate gas-flow restrictor and release valve.
The inventive method may further provide for conducting at least one gas pressure measurement in the pneumatic circuit upstream of the inflatable cuff (e.g. via the use of a second gas pressure measurement means). Such upstream pressure measurement(s) may then be utilized with the downstream pressure measurement(s) to determine a measurement, e.g. a value corresponding with a ratio therebetween. In turn, such ratio value may be utilized in the cuff identification step.
In another aspect of the inventive method, the inflating step may provide for the inflation of a cuff to a degree corresponding with a first predetermined pressure (e.g. as measured by the first pressure measurement means), and the deflating step may provide for cuff deflation to a degree corresponding with at least a second predetermined pressure. The obtainment of downstream pressure measurement(s) may be terminated upon at least one of two conditions. First, the obtaining step may be terminated when the inflatable cuff has deflated to a degree corresponding with the second predetermined pressure. Alternatively, the obtaining step may be terminated when a predetermined amount of time has lapsed after initiation of the deflating step. Preferably, the obtaining step will be terminated upon the earliest of the two above-noted conditions.
In one arrangement, the inventive method provides for the obtainment of a plurality of pressure measurements both upstream and downstream of the inflatable cuff during the deflating step, such upstream and downstream pressure measurements being obtained in a synchronous , paired fashion. The pairs of upstream and downstream pressure measurements are then utilized to determine a corresponding plurality of ratio values. The plurality of ratio values may be utilized in a predetermined algorithm to determine an average ratio value, a maximum ratio value and a minimum ratio value. The average ratio value may be employed to identify the inflatable cuff being utilized, which in turn allows for the automatic selection of an appropriate initial inflation pressure to be utilized in the actual blood pressure measurement procedure that follows. In this regard, the average ratio value may be compared with predetermined reference ratio value ranges (e.g. corresponding with each potential cuff to be identified) in the cuff identification operation. For example, cuff #1 (e.g. for neonates) may have a first predetermined reference value range; cuff #2 (e.g. for children) may have a second predetermined reference value range that is greater than the first range and separated therefrom by a predetermined xe2x80x9cguard bandxe2x80x9d; cuff #3 (e.g. for adults) may have a third predetermined ratio value range that is greater than the first and second ranges and separated from the second range by a predetermined xe2x80x9cguard bandxe2x80x9d; and cuff #4 (e.g. for obese patients) may have a fourth predetermined ratio value range that is greater than the first, second and third ranges and separated from the third range by a predetermined xe2x80x9cguard bandxe2x80x9d. In the event that a given average ratio value falls within a xe2x80x9cguard bandxe2x80x9d, the method may provide for reinitiation of the cuff identification operation and/or termination of the operation with an indication provided to the user (e.g. a message display after a predetermined sequence of xe2x80x9cguard bandxe2x80x9d readings).
The maximum and minimum measured ratio values may be employed to ensure the integrity of the cuff identification. That is, for example, if the difference between the maximum ratio value and the minimum ratio value exceeds a predetermined reference value, the cuff identification operation may be reinitiated and/or a corresponding indicator may be otherwise provided to a user (e.g. a display message after a predetermined number of iterations).
In accordance with the described arrangement, the inventive method may further provide for a predetermined delay period between the inflation step and the deflation step of the cuff identification operation. During such predetermined time period, gas pressure measurements may be obtained both upstream of the inflatable cuff and downstream of the inflatable cuff (e.g. via the first and second measurement means). Such measurements may then be compared to ensure the integrity of the pneumatic circuit. In the event that such comparison indicates a difference that exceeds a predetermined reference value, the method may provide for an automatic response. By way of example, such response may include the provision of an indication to a user (e.g. to check for pneumatic line kinks, etc.), reinitiation of the cuff identification operation and/or termination of the cuff identification operation.
In conjunction with the present invention, an inventive apparatus is also provided for identifying at least one inflatable cuff interconnectable to a sphygmomanometer. The apparatus comprises inflation and deflation means, interconnectable in a pneumatic circuit with an interconnectable inflatable cuff, for selectively inflating and deflating the cuff. The apparatus further includes a processor preprogrammed to automatically receive at least one pressure measurement from a first pressure measurement means in the pneumatic circuit during operation of the deflation means in a cuff identification operation. The processor is further preprogrammed to automatically employ the pressure measurement to identify the given inflatable cuff interconnected to the apparatus. Preferably, the first pressure measurement means is located in the pneumatic circuit downstream of the interconnectable cuff.
As will be appreciated, the processor means may be operatively interconnected with the inflation means and deflation means and preprogrammed to control the operation of each in the cuff identification operation. More particularly, the processor means may be preprogrammed to successively operate an air pump comprising the inflation means, and open a bleed valve comprising a deflation means.
The inventive apparatus may further include a second pressure measurement means for obtaining at least one pressure measurement in the pneumatic circuit upstream of the interconnectable inflatable cuff. The second pressure measurement means may also be interconnected with the processor means, wherein the processor is preprogrammed to automatically receive at least one upstream pressure measurement (i.e. relative to the inflatable cuff) and at least one downstream pressure measurement (i.e. relative to the inflatable cuff), and to automatically calculate a ratio therebetween. Most preferably, a plurality of upstream and downstream pressure measurements will be synchronously obtained by the processor in corresponding pairs, wherein each pair is utilized to determine a corresponding ratio value for use in cuff identification.
Of note, the interconnectable inflatable cuff may be fixedly and pneumatically attached to a first gas-flow restricting means (e.g. a gas orifice), wherein the first gas-flow restricting means restricts the flow of gas therethrough at a predetermined resistive level. In this regard, the inventive apparatus may be provided to identify any given one of a predetermined plurality of inflatable cuffs when interconnected in the pneumatic circuit, wherein each of the predetermined plurality of inflatable cuffs is fixedly and pneumatically interconnected to a corresponding one of a plurality of gas-flow restricting means, each of said gas-flow restricting means being different.
To normalize the various pressure measurements obtainable in conjunction with cuff identification, the inventive apparatus may further include a second gas-flow restricting means. More particularly, the second gas-flow restricting means may be located in the pneumatic circuit downstream of the interconnectable cuff, first gas-flow restricting means, and/or second pressure measurement means. As noted, the second gas-flow restricting means may comprise a bleed valve. When a separate restrictor and bleed valve are employed, the restrictor means may be provided upstream of the bleed valve.
In view of the foregoing, it should be appreciated that an overall inventive system may also be provided for use in obtaining blood pressure measurements. Such system may include a predetermined plurality of inflatable cuffs, each of the predetermined cuffs being fixedly and pneumatically interconnected to a corresponding one of a plurality of gas-flow restricting means, wherein each of the gas-flow restricting means restricts the flow of gas therethrough to a differing degree. The system may further include a monitor that is pneumatically interconnectable to any one of the predetermined plurality of inflatable cuffs. The monitor may house inflation means and deflation means for selectively inflating and deflating, respectively, a given, interconnected one of the predetermined plurality of inflatable cuffs. The monitor is operable to automatically identify the given connectable one of the predetermined plurality of inflatable cuffs based upon at least one pressure measurement obtained during operation of the deflation means in a cuff identification operation. The monitor may include first and second pressure measurement means, as previously noted, to obtain a corresponding plurality of upstream and downstream pressure measurements (i.e. relative to the given interconnected inflatable cuff). Outputs from the first and second pressure measurement means may then be employed (e.g. in a ratio value) to provide a relative measure of the pressure drop between the first and second pressure measurement means across the gas-flow restricting means of the given interconnected, inflatable cuff. Again, a processor may be provided for automatically controlling operation of the inflation means and deflation means, for automatically receiving measurements from the first and second pressure measurement means, and for automatically utilizing the measure values to identify the interconnected cuff.
Numerous advantages are provided by the present invention. In particular, the inventive method and apparatus accommodate the use of varying lengths of pneumatic lines to interconnect a cuff and a monitor while monitoring accuracy in cuff identification. Similarly, the present invention yields high accuracy regardless of variations in the tightness or quality of the wrap of a given cuff about a patient appendage. Similarly, accuracy of the present invention is maintained despite wear of the inflation means employed (e.g. an air pump). Finally, the present invention is relatively easy and inexpensive to implement and lends itself to a variety automated approaches for enhancing overall reliability. Numerous additional advantages and aspects of the present invention will become apparent upon consideration of the further description that follows.